Obstructive sleep apnea is a serious disorder in which normal breathing during sleep is interrupted for periods of 10 seconds to a minute or even longer as a result of obstruction of the upper airway. Sleep apnea syndrome also involves decreases in blood oxygen levels. To resume breathing and restore blood oxygen, the subject must wake up. Thus, normal sleep is interrupted. Sleep apnea may be classified as mild, five to 25 events per hour; moderate, 25 to 40 events per hour; or severe more than 40 events per hour. Persons with sleep apnea are prevented from attaining essential rest and suffer from chronic sleep fragmentation/deprivation occurring as a consequence of frequent nightly arousals brought about by critical decreases in blood oxygen levels secondary to disruptions in respiration. It has been estimated that from 1 to 3 percent of the adult population of North America suffers from sleep apnea. Sleep apnea has been associated with increased risk of heart attacks or strokes. Sleep apnea sufferers also frequently experience excessive daytime sleepiness which can result in them suddenly falling asleep while engaged in activities requiring alertness, such as driving a car.
Although consideration has been given to the possibility of treating sleep apnea with drugs such as medroxyprogesterone, protriptyline, acetazolamide, nicotine or even strychnine, there is currently no satisfactory pharmacotherapy for sleep apnea. Instead, sleep apnea is commonly treated either by throat surgery designed to maintain airway patency during sleep or with mechanical devices such as dental retainers. Surgery to remove tissues thought to contribute to obstruction of the airway is effective in only about 50 to 60% of patients. Cases of obstructive sleep apnea are generally managed with apparatus known as a continuous positive airway pressure (CPAP) machine. The CPAP comprises a mask that fits over the nose of the patient. The mask has an hose attached to it and a small box with a fan that blows air through the hose and into the nasal passages. The CPAP machine provides positive air pressure in the patient airway in order to prevent collapse of the airway which initiates a sleep apnea episode. While the CPAP is generally effective if used consistently, it is also expensive, cumbersome and highly inconvenient, thereby giving rise to significant patient compliance problems.
Thus, there has remained a substantial need for improved methods of treating obstructive sleep apnea, and particularly for an effective pharmacotherapy for treating this disorder.